Stoichiometric Alkane and Aldehyde Hydroxylation Reactions Mediated by In Situ Generated Iron(III)-Iodosylbenzene Adduct

Previously synthesized and spectroscopically characterized mononuclear nonheme, low-spin iron(III)-iodosylbenzene complex bearing a bidentate pyridyl-benzimidazole ligands has been investigated in alkane and aldehyde oxidation reactions. The in situ generated Fe(III) iodosylbenzene intermediate is a reactive oxidant capable of activating the benzylic C-H bond of alkane. Its electrophilic character was confirmed by using substituted benzaldehydes and a modified ligand framework containing electron-donating (Me) substituents. Furthermore, the results of kinetic isotope experiments (KIE) using deuterated substrate indicate that the C-H activation can be interpreted through a tunneling-like HAT mechanism. Based on the results of the kinetic measurements and the relatively high KIE values, we can conclude that the activation of the C-H bond mediated by iron(III)–iodosylbenzene adducts is the rate-determining step.

Properties such as charge, stereochemistry, inductive effects, and soft/hard characteristics all affect the relative stability of the Fe(II) versus the Fe(III) state and, thus, the Fe(II/III) redox potential. The cyclic voltammogram of 1 exhibits quasi reversible redox waves for the Fe II /Fe III couple at +0.902 V (Epa = +0.934 V; Epc = +870 mV vs. Ag/AgCl). This is not surprising since neutral ligands tend to move the potential more positively and We have found previously that µ-1,2-peroxo-diiron(III) intermediates with N-heterocyclic ligands such as 2-(2-pyridyl)benzimidazole (PBI), 2-(2-pyridyl)-N-methylbenzimidazole (MeBIP) and 2-(4-thiazolyl)benzimidazole (TBI) have ambiphilic character [25][26][27][28]. They can deformylate aldehydes via nucleophilic mechanism as mimics for aldehyde deformylase oxygenase (cADO), and oxidize 2,6-DTBP via electrophilic mechanism as mimics for ribonucleotid reductases (RNR-R2) [28]. They are also available for oxidative N-demethylation of DMA via electrophilic C-H activation [27]. Spectral properties, reactivity and kinetics of Fe III OIPh (2) bearing PBI ligands towards cycloketones in nucleophilic Baeyer-Villiger reactions were investigated in detail [19]. The question arises whether Fe III OIPh has ambiphilic properties, and whether it can participate in electrophilic reactions. In this study, we investigate the reactivity of the previously reported (PBI)Fe III OIPh intermediate and its methyl-substituted derivative ((4Me-PBI)Fe III OIPh) towards benzaldehydes. The results of detailed kinetic measurements are compared to each other and with the results observed for the nucleophilic [Fe III 2 (µ-1,2-O 2 )(PBI) 4 (S 2 )] 4+ intermediate (Scheme 1). The mechanism and the key role of the Fe III OIPh intermediate is proposed based on detailed kinetic measurements including KIE and Hammett data. These complexes exhibit electrophilic reactivity in the oxidation of C-H bond of benzaldehydes, and are also capable of oxidizing the triphenylmethane, further evidence of their electrophilic nature.

Results and Discussions
As previously reported, [ ). Furthermore, it is worth noting that the iodosylbenzene adduct (2) does not form again upon addition of PhIO, indicating that 2 dec is probably the death and of the oxidant. The formation mechanism and composition of 2 are currently not clear, but based on its decomposition product, the following structure can be proposed, [Fe III (OH)(OIPh)(PBI) 2 ](CF 3 SO 3 ) 2 .
Properties such as charge, stereochemistry, inductive effects, and soft/hard characteristics all affect the relative stability of the Fe(II) versus the Fe(III) state and, thus, the Fe(II/III) redox potential. The cyclic voltammogram of 1 exhibits quasi reversible redox waves for the Fe II /Fe III couple at +0.902 V (E pa = +0.934 V; E pc = +870 mV vs. Ag/AgCl). This is not surprising since neutral ligands tend to move the potential more positively and stabilize the ferrous state, particularly if they are strong field ligands such as o-phenanthroline Molecules 2023, 28, 1855 3 of 13 (E • = 1.14 V) and PBI. Then, the voltammogram of the reactive species 2 was measured by adding PhIO to the solution of 1, (Figure 1b). We found that the Fe II /Fe III couple (1) was disappeared, and new reversible redox waves appeared at −0.115 V (E pa = −0.076 V; E pc = −0.153 mV vs. Ag/AgCl), corresponded to Fe II /Fe III couple of 2 ( Figure 1b). This significant shift is consistent with the replacement of one neutral soft PBI ligand with a hard neutral and negatively charged ligands, such as PhIO and OH -, which stabilize the ferric state relative to the ferrous state.
stabilize the ferrous state, particularly if they are strong field ligands such as o-phenanthroline (E° = 1.14 V) and PBI. Then, the voltammogram of the reactive species 2 was measured by adding PhIO to the solution of 1, (Figure 1b). We found that the Fe II /Fe III couple (1) was disappeared, and new reversible redox waves appeared at −0.115 V (Epa = −0.076 V; Epc = −0.153 mV vs. Ag/AgCl), corresponded to Fe II /Fe III couple of 2 ( Figure 1b). This significant shift is consistent with the replacement of one neutral soft PBI ligand with a hard neutral and negatively charged ligands, such as PhIO and OH -, which stabilize the ferric state relative to the ferrous state.
The ESI-MS spectrum of the iron product formed in the reaction of 2 with PhCHO or Ph3CH shows that Fe(III), mainly Fe(III)-hydroxide ([(PBI)2Fe III (OH)(OEt)] + ; m/z = 508.13), was the main iron product. To verify the feasibility of reaction between Fe(III) or Fe(II) species in the mixture solution, when PhIO was added to the complete reaction solution obtained after the reaction of 2 with PhCHO or Ph3CH, no reformation of 2 was detected. The reactivity of the in situ generated Fe III OIPh (2) adduct was investigated in the C-H bond activation of p-substituted benzaldehydes and triphenylmethane at 293 K in CH 3 CN. 2 reacted readily with aldehyde and triphenylmethane afforded benzoic acid and triphenylmethanol, respectively, as evidenced by gas chromatography mass spectrometry (GC-MS). The oxidation of PhCHO and Ph 3 CH by 2 under argon atmosphere yielded benzoic acid (80%), and triphenylmethanol (90%) (Scheme 2). We also investigated the possible effect of the formed products, namely, PHCO 2 H and Ph 3 CHOH, on the decomposition rate of FeOIPh. It can be concluded that in the case of 1 and 5 equivalents of PhCO 2 H and Ph 3 CH, the reaction rate hardly differs from the self-decomposition rate of the complex 2. Furthermore, these values are negligible compared to the values obtained during the investigated oxidation reactions towards PhCHO and Ph 3 CH (Tables 1 and 2). First-order rate constants (kobs) were determined by plotting the change (decrease) in the absorbance of the λmax = 760 nm feature of 2 against time (Figure 2a), and fitting the resulting curve under pseudo-first-order conditions (Figure 2b). First-order-rate constants (kobs' = kobs -ksd) values increased linearly with increasing PhCHO and Ph3CH concentra-      The ESI-MS spectrum of the iron product formed in the reaction of 2 with PhCHO or Ph 3 CH shows that Fe(III), mainly Fe(III)-hydroxide ([(PBI) 2 Fe III (OH)(OEt)] + ; m/z = 508.13), was the main iron product. To verify the feasibility of reaction between Fe(III) or Fe(II) species in the mixture solution, when PhIO was added to the complete reaction solution obtained after the reaction of 2 with PhCHO or Ph 3 CH, no reformation of 2 was detected.

Entry [1] (mM) Ph 3 CH (mM) T (K)
First-order rate constants (k obs ) were determined by plotting the change (decrease) in the absorbance of the λ max = 760 nm feature of 2 against time (Figure 2a), and fitting the resulting curve under pseudo-first-order conditions (Figure 2b). First-order-rate constants (k obs ' = k obs -k sd ) values increased linearly with increasing PhCHO and Ph 3 CH concentrations, giving rise to a second-order rate constant of 1.44 × 10 −1 M −1 s −1 and 6.54 × 10 −1 M −1 s −1 at 293 K, respectively (Tables 1 and 2), demonstrating that Ph 3 CH is more reactive than PhCHO (Figure 3a). A k rel = k 2 Ph3CH /k 2 PhCHO value of 4.5 was also determined by comparing the individual reactions under identical conditions. This species is more stable but exhibited much lower reaction rates than that were found in the reaction of the previously reported mononuclear Fe(OIPh)(13-TMC)(CF 3 CH 2 O)(CF 3 SO 3 )] + (13-TMC = 1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclotridecane) with Ph 3 CH (1.8 M −1 s −1 at 233 K) [13]. tions, giving rise to a second-order rate constant of 1.44 × 10 −1 M −1 s −1 and 6.54 × 10 −1 M −1 s −1 at 293 K, respectively (Tables 1 and 2), demonstrating that Ph3CH is more reactive than PhCHO (Figure 3a). A krel = k2 Ph3CH /k2 PhCHO value of 4.5 was also determined by comparing the individual reactions under identical conditions. This species is more stable but exhibited much lower reaction rates than that were found in the reaction of the previously reported mononuclear Fe(OIPh)(13-TMC)(CF3CH2O)(CF3SO3)] + (13-TMC = 1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclotridecane) with Ph3CH (1.8 M −1 s −1 at 233 K) [13].  A kinetic isotope effect (KIE = k2 PhCHO /k2 PhCDO ) of 11.5(3) was obtained for the oxidation of benzaldehyde by 2 (Figure 4a). This value is larger than "classical" KIE values (KIE ~ 7), but significantly smaller than that was observed for the reaction of [Fe Table 3). This result suggests that C-H activation can be interpreted via a tunneling-like HAT mechanism. In contrast to the [Fe III (OIPh)(13-TMC)(CF3CH2O)(CF3SO3)]+ system, where the intermediate was very unstable and decomposed into iron(IV)-oxo complex, we found no evidence for the formation of Fe IV O species [13]. However, the formation and participation of reactive high-valent oxoiron(IV or V) species in these oxidation reactions cannot be completely ruled out, but based on the results of the kinetic measurements and the relatively high KIE values, we can conclude that the activation of the C-H bond mediated by iron(III)-iodosylbenzene adducts is the rate-determining step. Unfortunately, we could not isolate the Fe IV O complex indirectly, so its reactivity cannot be compared with that of the adduct.  (Figure 3b). The Gibbs energy of 80 kJ mol −1 calculated for Ph 3 CH is smaller than that observed for PhCHO (83 kJ mol −1 ), which is consistent with the higher reactivity of Ph 3 CH due to its smaller C-H bond dissociation energy value.
A kinetic isotope effect (KIE = k 2 PhCHO /k 2 PhCDO ) of 11.5(3) was obtained for the oxidation of benzaldehyde by 2 (Figure 4a). This value is larger than "classical" KIE values (KIE~7), but significantly smaller than that was observed for the reaction of  (Table 3). This result suggests that C-H activation can be interpreted via a tunneling-like HAT mechanism. In contrast to the [Fe III (OIPh)(13-TMC)(CF 3 CH 2 O)(CF 3 SO 3 )]+ system, where the intermediate was very unstable and decomposed into iron(IV)-oxo complex, we found no evidence for the formation of Fe IV O species [13]. However, the formation and participation of reactive high-valent oxoiron(IV or V) species in these oxidation reactions cannot be completely ruled out, but based on the results of the kinetic measurements and the relatively high KIE values, we can conclude that the activation of the C-H bond mediated by iron(III)-iodosylbenzene adducts is the rate-determining step. Unfortunately, we could not isolate the Fe IV O complex indirectly, so its reactivity cannot be compared with that of the adduct. 7), but significantly smaller than that was observed for the reaction of [Fe IV (N4Py)(O)] 2+ (N4Py = N,N'-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine) and PhCH(D)O (KIE = 26.5) [11] (Table 3). This result suggests that C-H activation can be interpreted via a tunneling-like HAT mechanism. In contrast to the [Fe III (OIPh)(13-TMC)(CF3CH2O)(CF3SO3)]+ system, where the intermediate was very unstable and decomposed into iron(IV)-oxo complex, we found no evidence for the formation of Fe IV O species [13]. However, the formation and participation of reactive high-valent oxoiron(IV or V) species in these oxidation reactions cannot be completely ruled out, but based on the results of the kinetic measurements and the relatively high KIE values, we can conclude that the activation of the C-H bond mediated by iron(III)-iodosylbenzene adducts is the rate-determining step. Unfortunately, we could not isolate the Fe IV O complex indirectly, so its reactivity cannot be compared with that of the adduct.   Table 1).
These results clearly indicate that the rate-determining step in the reaction of 4R-PhCHO with peroxo-intermediates is nucleophilic attack. To investigate the nature of iron(III)iodosylbenzene adducts, we also investigated the electronic effect of para-substituents on the oxidation of benzaldehydes; 2 was treated with para-substituted benzaldehydes, para-R-PhCHO (R = NMe 2 , Me, H, Cl, and CN). A Hammett plot of the second-order rate constants versus σ p of substrates gave a ρ value of −0.76, demonstrating the electrophilic character of the iron(III)-iodosylbenzene adducts in HAT reactions. This value is little bit smaller than that observed for the reaction of [Fe IV (N4Py)(O)] 2+ and 4R-PhCHO (ρ = −1.21) [11] ( Table 3).
The The cyclic voltammogram of 3, similar to 1, exhibits quasi reversible redox waves for the Fe II /Fe III couple at +0.799 V (E pa = +0.840 V; E pc = +761 mV vs. Ag/AgCl). As a result of the methyl-substituent, a negative shift of 103 mV can be observed (Figure 5a). When the voltammogram of the reactive species 4 was measured by adding PhIO to the solution of 3, (Figure 5b). We found that the Fe II /Fe III couple (3)  In order to obtain more information about the effect of the methyl substituent on the reactivity towards C-H activation reactions, we have carried out detailed kinetic measurements for the in situ generated iron(III)-iodosylbenzene complex, 4, under identical conditions with the PBI-containing systems, above (Figure 6a) (Tables 3-5).
When the reaction rates of 2 and 4 were compared under the same conditions, the reaction rates were approximately threefold for benzaldehyde and twofold for triphenylmethane in favor of 2 due to the negative effect of the methyl substituent (Tables 3-5). This can be explained by the fact that the electron-donating methyl groups increase the electron density of the metal center and, thereby, reduce its electrophilic power. The decrease in the redox potential of complex 4 (and 3) is also consistent with the increase in electron density on the iron center ( Figure 5). A kinetic isotope effect (KIE = k2 PhCHO /k2 PhCDO ) of 14.1(5) is comparable to that was observed in the reaction of 2 and PhCHO, suggesting the same rate-determining steps (Table 4 and Figure 6b).  (Table 4).
A linear free-energy relationship between the second-order rate constants for the para-substituted 4R-PhCHO (R = NMe2, OMe, Me, H, F, Cl, CN, NO2) oxidations resulted in a negative ρ value of −0.56. This value is close to the data calculated for the 2/4R-PhCHO system, suggesting a similar mechanism including an electrophilic benzylic C-H activation on the aldehyde in the rate-determining step (Table 4 and Figure 7a). The activation parameters for PhCHO and Ph3CH are ΔE ‡ = 34(2) kJ mol −1 , ΔH ‡ = 31(3) kJ mol −1 , ΔS ‡ = −183(8) J mol −1 K −1 and ΔG ‡ = 85(5) kJ mol −1 , and ΔE ‡ = 72(5) kJ mol −1 , ΔH ‡ = 70(6) kJ mol −1 , ΔS ‡ = −40(10) J mol −1 K −1 ,and ΔG ‡ = 82(5) kJ mol −1 at 293 K, respectively. The Gibbs energy of 82 kJ mol −1 calculated for Ph3CH is smaller than that was observed for PhCHO (85 kJ mol −1 ), which is consistent with the higher reactivity of Ph3CH due to its smaller C-H bond dissociation energy value. These values are larger than those found for the reaction of 2 with Ph3CH (80 kJ mol −1 ) and PhCHO (82 kJ mol −1 ), which is consistent with the difference in the reactivity of the two complexes 2 and 4. Based on the temperature dependence of the reactivity of 2 and 4 towards PhCHO and Ph3CH, the determined values of -TΔS ‡ in  (Table 4). Table 4. Kinetic data for the 4-mediated stoichiometric oxidation of benzaldehydes in CH 3 CN.  When the reaction rates of 2 and 4 were compared under the same conditions, the reaction rates were approximately threefold for benzaldehyde and twofold for triphenylmethane in favor of 2 due to the negative effect of the methyl substituent (Tables 3-5). This can be explained by the fact that the electron-donating methyl groups increase the electron density of the metal center and, thereby, reduce its electrophilic power. The decrease in the redox potential of complex 4 (and 3) is also consistent with the increase in electron density on the iron center ( Figure 5). A kinetic isotope effect (KIE = k 2 PhCHO /k 2 PhCDO ) of 14.1(5) is comparable to that was observed in the reaction of 2 and PhCHO, suggesting the same rate-determining steps (Table 4 and Figure 6b).

Entry [1] (mM) 4R-PhCHO (mM) T (K)
A linear free-energy relationship between the second-order rate constants for the para-substituted 4R-PhCHO (R = NMe 2 , OMe, Me, H, F, Cl, CN, NO 2 ) oxidations resulted in a negative ρ value of −0.56. This value is close to the data calculated for the 2/4R-PhCHO system, suggesting a similar mechanism including an electrophilic benzylic C-H activation on the aldehyde in the rate-determining step (Table 4 and Figure 7a). The activation parameters for PhCHO and Ph 3 CH are ∆E ‡ = 34(2) kJ mol −1 , ∆H ‡ = 31(3) kJ mol −1 , ∆S ‡ = −183(8) J mol −1 K −1 and ∆G ‡ = 85(5) kJ mol −1 , and ∆E ‡ = 72(5) kJ mol −1 , ∆H ‡ = 70(6) kJ mol −1 , ∆S ‡ = −40(10) J mol −1 K −1 ,and ∆G ‡ = 82(5) kJ mol −1 at 293 K, respectively. The Gibbs energy of 82 kJ mol −1 calculated for Ph 3 CH is smaller than that was observed for PhCHO (85 kJ mol −1 ), which is consistent with the higher reactivity of Ph 3 CH due to its smaller C-H bond dissociation energy value. These values are larger than those found for the reaction of 2 with Ph 3 CH (80 kJ mol −1 ) and PhCHO (82 kJ mol −1 ), which is consistent with the difference in the reactivity of the two complexes 2 and 4. Based on the temperature dependence of the reactivity of 2 and 4 towards PhCHO and Ph 3 CH, the determined values of -T∆S ‡ in most cases were lower than ∆H ‡ in the investigated temperature range, indicating enthalpy-driven reactions. As a result of the compensation effect, the increasing activation enthalpies are offset by the increasingly positive entropies, giving ∆H ‡ = 79.8 kJ mol −1 at the intersection, which is little bit higher than that was obtained for the conversion of Fe III OOtBu intermediates to Fe IV O through O-O bond homolysis (∆H ‡ = 61.3 kJ mol −1 ) [29]. The experimentally determined difference between ∆G ‡ values is around 5 kJ mol −1 . Finally, the ∆G ‡ values were used to compare the reaction rates, and based on these, the relative reactivities of 2 and 4 toward PhCHO and Ph 3 CH show the following order: Ph 3 CH/2 > Ph 3 CH/4 > PhCHO/2 > PhCHO/4 ( Figure 7b). Based on the available information and reaction rate data, the reaction of benzaldehyde according to the electrophilic Fe III OIPh-based and nucleophilic [Fe III 2(μ-1,2-O2)(MPBI)4(S2)] 4+ -based mechanisms can also be compared. Based on these, it can be concluded that the nucleophilic, Baeyer-Villiger-type oxidation of benzaldehyde (2.39 M −1 s −1 ) is 32 times faster than the electrophilic hydroxylation of benzaldehyde (0.073 M −1 s −1 ) via C-H activation under identical conditions (Table 3). Based on the available information and reaction rate data, the reaction of benzaldehyde according to the electrophilic Fe III OIPh-based and nucleophilic [Fe III 2 (µ-1,2-O 2 )(MPBI) 4 (S 2 )] 4+ -based mechanisms can also be compared. Based on these, it can be concluded that the nucleophilic, Baeyer-Villiger-type oxidation of benzaldehyde (2.39 M −1 s −1 ) is 32 times faster than the electrophilic hydroxylation of benzaldehyde (0.073 M −1 s −1 ) via C-H activation under identical conditions (Table 3).

Materials and Methods
All chemicals including PBI and 4Me-PBI ligands obtained from Aldrich Chemical Co. and used without further purification unless otherwise indicated. Solvents were dried according to published procedures and distilled, stored under argon [30].
[Fe(PBI) 3 ](CF 3 SO 3 ) 2 (1) was synthesized according to literature methods [18]. Iodosylbenzene (PhIO) was prepared by literature methods [31]. UV-visible spectra were recorded on an Agilent 8453 diode-array spectrophotom-eter using quartz cells. IR spectra were recorded using a Thermo Nicolet Avatar 330 FT-IR instrument (Thermo Nicolet Corporation, Madison, WI, USA). Samples were prepared in the form of KBr pellets. GC analyses were performed on an Agilent 6850 (Budapest, Hungary) gas chromatograph equipped with a flame ionization detector and a 30 m HP-5MS column. GC-MS analyses were carried out on Shimadzu QP2010SE (Budapest, Hungary) equipped with a secondary electron multiplier detector with conversion dynode and a 30 m HP5MS column. Cyclic voltammetric experiments were carried out using an SP-150 potentiostat, using the EC-Lab V11.41 software. During the measurements, we used a three-electrode setup, we used a 3.0 mm diameter glassy-carbon electrode as working electrode, a Pt wire as counter electrode and an Ag/AgCl (3M KCl) reference-electrode. The supporting electrolyte was 0.1 M solution of tetrabutylammonium perchlorate.

Reactivity Studies and Product Analysis
All reactions were run in 1.0 cm UV cuvette and followed by monitoring UV-vis spectral changes in the reaction solutions, and rate constants were determined under pseudo-first-order conditions (e.g., [substrate]/[2] > 10) by fitting the absorbance changes at 760 nm for 2 was prepared by treating 1 (0.5 mM) with 1.2 equivalent of PhIO (dissolved in EtOH) in CH 3 CN at 278-298 K, respectively, and the resulting solutions were used directly in reactions with substrates, such as triphenylmethane, and benzaldehydes, for C-H bond activation reactions. Reactions were run at least in triplicate, and the data reported are the average of the reactions. ESI-MS spectra of the iron product formed in the reaction of 2 with triphenylmethane or benzaldehyde exhibited mainly Fe(III)-hydroxide, [Fe III (OH)(PBI) 2 (OEt)] + species (m/z = 508.13).

Conclusions
The reactivity of in situ generated iron(III)-iodosylbenzene adduct with bidentate pyridyl-benzimidazole ligand (PBI) has been investigated in C-H activation processes as biomimics of nonheme iron enzymes. The decay of Fe III OIPh was affected by triphenylmethane and benzaldehyde, leading to triphenylmethanol and benzoic acid, respectively. Based on detailed kinetic and mechanistic studies (KIE = 11.54, and ρ = −0.76 for 4R-PhCHO), a highly reactive electrophilic Fe III OIPh species was suggested as reactive key species responsible for the HAT reactions. The formation and participation of reactive high-valent oxoiron(IV or V) species in these oxidation reactions cannot be completely ruled out, but based on the results of the kinetic measurements and the relatively high KIE values, we can conclude that the activation of the C-H bond mediated by iron(III)-iodosylbenzene aducts can be interpreted through a tunneling-like HAT mechanism in a rate-determining step. The electrophilic nature of the key intermediate was also confirmed from the side of the complex, using a substituted 4Me-pyridyl-benzimidazole ligand-containing system. It was found that the electron-donating methyl groups increase the electron density of the metal center and thereby reduces its electrophilic power. The decrease in the redox potential of the methyl-containing Fe(4Me-PBI) complex is also consistent with the increase in electron density on the iron center. This is an another example of metal-oxidant adducts, which capable of benzylic hydroxylation of alkanes and aldehydes with weak C-H bonds prior to the conversion into oxoiron(IV) intermediate. We have also demonstrated that the iron(III)-iodosylbenzene mediated electrophilic oxidation of benzaldehydes via C-H activation is less favored compared to the µ-1,2-peroxo-diiron(III) mediated nucleophilic, Baeyer-Villiger-type oxidation of benzaldehyde. Furthermore, based on the calculated ∆G ‡ data, the relative reactivity of 2 and 4 toward Ph 3 CH and PhCHO was determined. This study may provide important insights into the design of biologically inspired oxidation catalysts.